A five-year study will be conducted to accomplish the following objectives: (1) To evaluate the linear growth in children with chronic renal failure under treatment with 1,25-dihydroxyvitamin-D3 in a randomized, double-blind, carefully controlled, clinical trial. (2) To assess the long-term efficacy and safety of 1,25-dihydroxyvitamin-D3 therapy in children with chronic renal failure through meticulous comparison to a control group on conventional therapy, with particular attention to the rate of progression of chronic renal failure to ensure that 1,25-dihydroxyvitamin-D3 treatment does not exacerbate the primary disorder. (3) To provide long-term evaluation and follow-up of children with chronic renal insufficiency by means of nutritional biochemical indices and antropometric measurements that will yield information never before collected but urgently needed to reveal the extra-skeletal effects of 1,25-dihydroxyvitamin-D3 treatment.